There are many microorganisms that have a useful enzymatic activity, and such microorganisms are widely used in the production of functional food materials such as carbohydrates, amino acids, and phospholipids. Among these, there are known many microorganisms which can be used in the production of carbohydrate materials, particularly oligosaccharides, and for example, it has been reported that a galactooligosaccharide is produced by utilizing the β-galactosidase activity of yeast belonging to the genus Sporobolomyces singularis (PTL 1).
Generally speaking, a microorganism is killed by a heating treatment and then stored etc, however, in the case where a microorganism having an enzymatic activity as described above is subjected to a heating treatment, whilst the microorganism is killed, the enzymatic activity is significantly decreased, which is practically useless. Further, as a technique for killing a microorganism while maintaining the enzymatic activity, there has been reported a technique for killing a microorganism while maintaining the enzymatic activity in which a transformed microorganism is treated with a chemical such as an alcohol at 25 to 35° C. (PTL 2). However, this technique has a problem that the use thereof after killing the microorganism is limited because a genetically modified microorganism is used or the alcohol or the like used in the treatment for killing the microorganism remains.